4) Less power consumption. Since the core's decryption is no longer in use.

5) Better all around benchmark scores.

The only way to temporarily decrypt encrypted ROMs on the fly is with an official BIOS or boot rom & firmware or flash file. ROMs either encrypted or decrypted, a BIOS, etc does sync performance & accuracy timing to better emulate the original source hardware.

Most ROMs on the internet are already decrypted. You wouldn't be able to run them without the official BIOS & firmware when they're encrypted. An easy way to check is to scan the file directory(ies) where you've your ROMs, ISOs & Eboots placed. By using Retorarch's file scanner.